The list of featured-article criteria calls for citations where appropriate. This page clarifies that requirement. This list is not exhaustive, and the examples are suggestions only. Each case must be dealt with on its merits.

You should always add a citation when quoting published material, and the citation should be placed directly after (or just before) the quotation, which should be enclosed within double quotation marks — "like this" — or single quotation marks if it is a quote-within-a-quote — "and here is such a 'quotation' as an example." For long quotes, you may wish to use Quotation templates.

Biographies of living persons should be sourced with particular care, for legal and ethical reasons. All contentious material about living persons must cite a reliable source. If you find unsourced or poorly sourced contentious material about a living person — whether in an article or on a talk page — remove it immediately! Do not leave it in the article while you request a source. Do not move it to the talk page. This applies whether the material is in a biography or any other article.

Images must include source details and a copyright tag on the image description page. It is important that you list the author of the image if known (especially if different from the source), which is important both for copyright and for informational purposes. Some copyright licenses require that the original author receive credit for their work. If you download an image from the web, you should give the URL:

There are a number of citation styles and systems used in different fields, all including the same information, with different punctuation use, and with the order of appearance varying for the author's name, publication date, title, and page numbers. Any style or system is acceptable on Wikipedia so long as articles are internally consistent. You should follow the style already established in an article, if it has one; where there is disagreement, the style or system used by the first editor to use one should be respected.

Articles can be supported with references in two ways: the provision of general references ("References") – books or other sources that support a significant amount of the material in the article – and inline citations ("Notes"), which are mandated by the featured article criteria and (to a lesser extent) the good article criteria. Inline citations are references within the text that provide source information for specific statements. They are appropriate for supporting statements of fact and are needed for statements that are challenged or likely to be challenged, including contentious material about living persons, and for all quotations.

All citation techniques require detailed full citations to be provided for each source used. Full citations must contain enough information for other editors to identify the specific published work you used.

Full citations for books typically include: the name of the author, the title of the book or article, the date of publication, and page numbers. The name of the publisher, city of publication, and ISBN are optional, although publisher is generally required for featured articles. For journal articles, include volume number, issue number (where the publication uses them) and page numbers. Citations for newspaper articles typically include the title of the article in quotes, the byline (author's name), the name of the newspaper in italics, date of publication, page number(s), and a comment with the date you retrieved it if it is online (invisible to the reader).

When citing books and articles, provide page numbers where appropriate. Page numbers should be included whenever possible in a citation that accompanies a specific quotation from, or a paraphrase or reference to, a specific passage of a book or article. The edition of the book should be included in the reference section, or included in the footnote, because pagination can change between editions. Page numbers are especially important in case of lengthy unindexed books. Page numbers are not required when a citation accompanies a general description of a book or article, or when a book or article, as a whole, is being used to exemplify a particular point of view.

According to The Oxford Style Manual, the author-date or Harvard system is the most commonly used reference method in the physical and social sciences (Ritter 2002). Author-date referencing can be especially useful when a single, large work has to be referenced by page number multiple times, as these separate citations would each require different footnotes.

Under the author-date referencing system, a reference source such as a book is cited in the text in parentheses, after the section, sentence, or paragraph for which the book was used as a source, using the surname of the author and the year of publication only, with the parentheses closing before the period, as in (Jones 2005). Page numbers must be included in a citation that accompanies a specific quotation from, or a paraphrase or reference to, a specific passage of a book or article. They usually follow the date in this way: (Author 2006:28) or (Author 2006, p.28).

A full reference is then placed at the end of the text in an alphabetized list of "References".

In article, common rules:

When the author of the reference is named as part of the text itself, put the year in parentheses; for example "Smith (2005) says..."

For two authors, use (Smith & Jones 2005); for three or more authors, use (Smith et al. 2005).

If the same author has published two books in 1996, and both are being referenced in the text, this is written as (Clancy 1996a) and (Clancy 1996b).

If the date of publication is unavailable, use "n.d." (meaning, no date)

Newspaper articles may use the name of the newspaper and the date of publication after the sentence (The Guardian, December 17, 2005).

A book published long after the original publication may be cited (Marx [1867] 1967).

For a quotation that is within the text and marked by quotation marks, the citation follows the end-quotation mark ("), and is placed before the period (.), "like this" (Smith 2005).

For a quotation that is indented, the citation is placed after the period, like the following. (Smith 2005)

In cases where the author is unknown:

If the article is written for an organization or periodical then use its name, as in (Department of Transport 2001) or (National Geographic 2005),

otherwise, use the article title, italicized, as in (Advertising in the Western Cape 1990:14).

In a "References" section at the end of the article:

For a book: in the case of (Author 2005a) and (Author 2005b), this might be:

Then one would link to the anchor: [[#Ritter2002|Ritter 2002]] throughout the text, if necessary providing a page number. Author-date referencing is particularly useful for works which must be repeatedly referenced by page number; in the case of footnotes, one must create an entirely new footnote for each different page.

A footnote is a note placed in the proper end section of a page to comment on a part of the main text, or to provide a reference (a source) for it. The connection between the relevant text and its footnote is indicated by a number or symbol which appears both after the relevant text and before the footnote. Footnotes are often used to add information that might be helpful to later fact-checkers, such as a quotation that supports your edit.

Place a <ref> ... </ref> where you want a footnote reference number to appear in an article—type the text of the note between the ref tags.

Place <references/> or {{reflist}} in an otherwise empty "Notes" or "References" section near the end of the article—the list of notes will be automatically generated here. If you want to create two columns of notes, write {{reflist|2}}.

Example edit:

The Sun is pretty big,<ref>Miller, E: "The Sun", page 23. Academic Press, 2005.</ref>
but the Moon is not so big.<ref>Brown, R: "Size of the Moon", ''Scientific American'', 51(78):46</ref>
The Sun is also quite hot.<ref>Miller, E: "The Sun", page 34. Academic Press, 2005.</ref>==Notes==<references/>

Example rendered result:

The Sun is pretty big,[1] but the Moon is not so big.[2] The Sun is also quite hot.[3]

Material may be referenced mid-sentence, but footnotes are usually placed at the end of a sentence or paragraph. Footnotes at the end of a sentence or phrase are normally placed immediately after the punctuation, except for dashes, as recommended by the Chicago Manual of Style and other style guides.[৩][৪] Some editors prefer the in-house style of journals such as Nature, which place references before punctuation. If an article has evolved using predominantly one style of ref tag placement, the whole article should conform to that style unless there is a consensus to change it.

When footnotes are used, some editors find it helpful to maintain a separate "References" section, in which the sources that were used are listed in alphabetical order. With articles that have a lot of footnotes, it can be hard to see which sources have been used, particularly when the footnotes contain explanatory text. An ordered "References" section helps readers to see at a glance which references were used.

When a separate reference section is included and full citations are listed there in alphabetical order, with the footnotes in a separate section entitled "Notes" or "Footnotes", then shortened notes may be used, giving the author(s), publication year, or perhaps the title, and the page numbers, in place of the full detail.

Because footnotes work by placing the required content inside <ref> tags within the article text they necessarily break up the text to some degree when in edit mode. Article text can become difficult to read and maintain. In this respect well referenced articles can unfortunately suffer disproportionately in comparison to those not so well sourced. In any case the disruptive effect can kept to a minimum by using shortened notes.

See the "Example edits for different methods" page for some comparative examples using shortened notes and full length references in footnotes. These offer representations of edit mode views with examples of how they render to the reader.

Another advantage of shortened notes is that they can be used in combination with source lists, like those used for general references. The disadvantage of those - that they do not tie to specific facts in the article - can thus be overcome.

Moreover, lists of sources ordered like in scientific articles (by author names, or in some cases by publication date) are easy to maintain and keep up to date by any user. Especially in well-sourced articles, footnoted references are not displayed in any particular order. In a monolithic reference list, is much easier to see at a glance whether a specific source has already been incorporated into the article.

And since the references are kept in one coherent block of code rather than strewn throughout the text, picking a specific source for further editing (e.g. adding ISBN, DOI or other detail) is also more convenient.

Web pages referenced in an article can be linked to directly by enclosing the URL in square brackets. For example, a reference to a newspaper article can be embedded like: [http://media.guardian.co.uk/site/story/0,14173,1601858,00.html], which looks like this: [১]

A full citation is also required in a References section at the end of the article. Providing an access date for the link in a comment helps editors recover a link that has become unavailable.

The use of citation templates is neither encouraged nor discouraged. Templates may be used or removed at the discretion of individual editors, subject to agreement with other editors on the article. Because templates can be contentious, editors should not change an article with a distinctive citation format to another without gaining consensus.

There are (at least) two families of citation templates. The {{Citation}} template is intended to provide citations for many types of references. The other family has names of the form {{Cite xxx}} (for example, {{Cite book}} and {{Cite web}}). These two families produce different citation styles. For example, the {{Cite xxx}} family separates elements with a full stop, and gives page ranges as plain numbers, while the {{Citation}} template separates elements with a comma, and precedes page ranges with "pp." Thus, these two families should not be mixed in the same article.

The {{Harv}} family of templates is available to produce author-date references in various formats with links matching the anchors produced by the {{Citation}} template. The following example constructs would produce references with different formatting styles having links matching the anchor produced by the example above:

It is possible to construct more exotic reference formats as well as to produce links with {{Harv}} family templates which match anchors produced by {{Cite xxx}} family templates (or any arbitrary anchor). The details are beyond the scope of this subsection, and can be found in the documentation of the individual templates.

An ==External links== or ==Further reading== section is placed near the end of an article and offers books, articles, and links to websites related to the topic that might be of interest to the reader. The section "Further reading" may include both online material and material not available online. If all recommended material is online, the section may be titled "External links".

All items used as sources in the article must be listed in the "References" or "Notes" section, and are usually not included in "Further reading" or "External links". However, if an item used as a reference covers the topic beyond the scope of the article, and has significant usefulness beyond verification of the article, you may want to include it here as well. This also makes it easier for users to identify all the major recommended resources on a topic. The Wikipedia guideline for external links that are not used as sources can be found in Wikipedia:External links.

A "convenience link" is a link to source material on the Web posted by someone other than the original publisher or author. For example, a newspaper article no longer available on the newspaper's website may be hosted elsewhere. When offering convenience links, it is important to be reasonably certain that the convenience copy is a true copy of the original, without any changes or inappropriate commentary, and that it does not infringe the original publisher's copyright. Accuracy can be assumed when the hosting website appears reliable, but editors should always exercise caution, and ideally find and verify multiple copies of the material for contentious items.

If an article has no references, and you are unable to find them yourself, you can tag the article with the template {{Unreferenced}}, so long as the article is not nonsensical or a WP:BLP, in which case request admin assistance. If a particular claim in an article lacks citation and is doubtful, consider placing {{fact}} after the sentence or removing it. Consider the following in deciding which action to take:

1. If a claim is doubtful but not harmful to the whole article or to Wikipedia, use the {{fact}} tag, but remember to go back and remove the claim if no source is produced within a reasonable time.

2. If a claim is doubtful and harmful, you should remove it from the article; you may want to move it to the talk page and ask for a source, unless you regard it as very harmful or absurd, in which case it should not be posted to a talk page either. Use your common sense. All unsourced and poorly sourced contentious material about living persons should be removed from articles and talk pages immediately. It should not be tagged. See Wikipedia:Biographies of living persons and Wikipedia:Libel.

When a link "goes dead" (see link rot and Wikipedia:Dead external links), it should be repaired or replaced, if possible. In most cases, one of the following approaches will give an acceptable alternative.

First, check the link to confirm that it is dead. The site may have been temporarily down or changed its linking structure. If the link has returned to service but has been labeled as a dead link, simply remove the labeling. See Template:dead link.

Find a copy of the referenced document. There may be a copy of the referenced document in a web archiving service. If so, update the dead link to point to the copy of the referenced document.

Find a substitute for the referenced document. Enter key words or phrases or other content from the cited material into the referenced website's search engine, into a similar website's search engine, or into a general search engine such as Google. (A search engine may hold a cached version of the dead link for a short time, which can help find a substitute.) Or, browse the referenced document's website or similar websites. If you find a new document that can serve as a substitute, update the dead link to refer to the new document.

Deactivate the dead link, and keep the citation information if still appropriate to the article. (This may happen, for example, when an online copy of material that originally appeared in print is no longer online.) In the remaining citation, note that the dead link was found to be inactive on today's date. Even with an inactive link, the citation still records a source that was used, and provides a context for understanding archiving delays or for taking other actions. In order to deactivate the dead link, do one of the following.

Turn the dead link into plain text. Remove only enough of the dead link's wikitext or markup language or URI scheme (square brackets, "http://", and so on) so that clicking on the link does not take you to its destination. This will make the link visible to both readers and editors of the article.

Turn the dead link into an HTML comment. Place HTML comment markup language around the link. This will make the link disappear when reading the article, but will preserve the link for editors of the article.

If a dead link cannot be repaired or replaced, consider reworking the article section so that it no longer relies on the dead link.

Whether a dead link can or cannot be repaired or replaced, remember that Wikipedia policy (including policy on sources and biographies of living persons) still applies. Consider doing further edits of the citation and cited material, if appropriate, to improve the article.

To help prevent dead links, consider citing reference sources using a persistent identifier such as a digital object identifier, if available; or consider archiving the referenced document online when writing the article section, if permitted by copyright. Also, consider avoiding links to web pages that usually disappear after short periods of time, such as at some news sites.

Wikicite is a free program that helps editors to properly reference their Wikipedia contributions using citation templates. It is written in Visual Basic .NET, making it suitable only for users with the .NET Framework installed on Windows, or, for other platforms, the Mono alternative framework. Wikicite and its source code is freely available, see the developer's page for further details.

User:Richiez has tools to automatically handle citations for a whole article at a time. Converts occurences of {{pmid XXXX}} or {{isbn XXXX}} to properly formatted footnote or harvard style references. Written in ruby and requires a working installation with basic libraries.

↑The Chicago Manual of Style, 14th ed. 1993, Clause 15.8, p. 494 - "The superior numerals used for note reference numbers in the text should follow any punctuation marks except the dash, which they precede. The numbers should also be placed outside closing parentheses." - See also CMoS Online, Style Q&A, Punctuation.